devargs: add dump command in test application

devargs: add dump command in test application

This is useful for debug purposes. Example:

echo 100 > /sys/devices/system/node/node0/hugepages/hugepages-2048kB/nr_hugepages
echo 100 > /sys/devices/system/node/node1/hugepages/hugepages-2048kB/nr_hugepages
./app/test -c 0x15 -n 3 -m 64 \
  --use-dev="eth_ring0" --use-device="eth_ring1" --use-device="02:00.0"
RTE>>dump_devargs
User device white list:
  VIRTUAL eth_ring0
  VIRTUAL eth_ring1
  PCI whitelist 0000:02:00.0

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>